Significant effort has been invested over the years in improving the capacity and power of electrical energy storage devices such as capacitors and batteries. Of particular interest herein are supercapacitors. These energy storage devices are particularly useful in short term, high power applications such as electric vehicles and wireless communication devices. A typical supercapacitor comprises carbon-based electrodes and a liquid electrolyte having charged ions which can be ordered around the electrodes to create a potential between the electrodes.
A liquid electrolyte typically comprises an ionic salt dissolved in a solvent. A wide variety of solvents and salts are available for such use, offering specific advantages depending on the application being considered (e.g., low temperature vs. high temperature). Generally, non-aqueous electrolytes are preferred from the standpoint of electrochemical stability and are considered herein in detail. A common nonaqueous electrolyte comprises a salt, e.g., tetraethyl ammonium tetrafluoroborate (TEABF4) or methyltriethyl ammonium tetrafluoroborate (MTEABF4), dissolved in an organic solvent, e.g., acetonitrile (AN), propylene carbonate (PC) or gamma butyrolactone (GBL). More recently, applicants have discovered that pyridinium tetrafluoroborate salt (PyHBF4) can be dissolved in certain known solvents, such as, propylene carbonate (PC), acetonitrile (AN), and gamma butyrolactone (GBL), to yield an electrolyte having an unexpectedly high conductivity and unexpectedly wide window of electrochemical stability.
Obviously, to be effective, the electrolyte must be contained within the electrochemical storage device. These devices sometimes leak electrolyte, however, due to an improper seal in assembly or damage after manufacture. Generally this leak is small and not noticeable. However, when the device is installed in the electronic/electrical systems, the electrolyte can cause corrosion of the components of the system, thereby ruining the system in which the device is placed. Therefore, there is a need to determine the existence of electrolyte leakage in the device before its installation in an electrical system.